The invention relates to an apparatus for producing and maintaining a suspension of solids and liquids. The invention is especially suitable for producing and maintaining of suspensions which have a tendency to separate, in other words, in which the solids tend to rapidly settle down at the bottom of the container, for example, glass beads in water.
In order to maintain solids suspended in a liquid, it is necessary to maintain a continuous whirling movement, especially where the components of the suspension have a different specific weight or density. Well known means for sustaining such a whirling motion comprise, for example, a stirring device such as a rotating propeller, mixing worms or agitators. Reference is made in this connection, for example, to German Pat. No. 2,248,851. It is also known to maintain suspensions by means of circulating pumps which continuously withdraw a portion of the content of a container by means of a pump which accelerates that proportion through a closed loop piping system back into the container. Yet another known method for producing and maintaining a suspension blows an air stream into the container. The air bubbles rising in the container keep the suspension in motion.
However, it has been found that known methods have certain disadvantages, especially where a uniform mixing ratio is to be produced and maintained in a container, having a length of several meters. Thus, if in such a long container several rotating agitating devices are arranged along the length of the container, so-called slack or dead zones are created between two rotating agitators and close to the container wall. In these slack or dead zones, the solids tend to settle to the bottom of the container. Even where circulating pumps are employed, slack or dead zones can also not be entirely avoided because a satisfactory whirling motion occurs only in the immediate vicinity of the nozzles through which the accelerated jet of the liquid is introduced. Even air bubbles do not work entirely satisfactory because there is a tendency that the solids clog the air exit openings and because dead zones are also created around the air jets so that a completely uniform agitation throughout the volume of the container is not possible.
In a known wet blasting apparatus which is used for blasting large work pieces, for example, having a length of 12 meters and a width of 2 meters, the work piece is clamped in such a position that its longitudinal extension is horizontal and its width extends vertically. The blasting medium is, for example, water mixed with glass beads and is accelerated through one or several jet nozzles toward the work piece. A coordinate control mechanism is employed to move the nozzles so as to cover each point of the work piece or structural member. One or several funnels are arranged below the work piece for capturing the blasting medium running off the structural member or work piece. Where several funnels are employed it is necessary to provide a pipe system for returning the blasting medium or mixture into a stationary mixing container where the mixture is subjected to a strong whirling action so that the blasting medium, in the form of a suspension, may be transported by means of pressure pumps to the jets through flexible hose conduits. It has been found that such a wet blasting apparatus has several disadvantages. On the one hand, it is necessary that the collecting funnel has side walls which are inclined at an angle of at least 45.degree.. Thus, if only one funnel is used, the apparatus has a rather large structural height, whereby it may become necessary to install the apparatus at two different floors or levels. On the other hand, where a plurality of collecting funnels are used, a rather expensive pipe conduit system must be used which is prone to trouble because depositions of the solids in the blasting medium cannot be prevented, whereby the system may not only be clogged but it is possible that such depositions conglomerate and return into the mixture in an uncontrolled manner, whereby the mixing ratio in the mixing container is influenced in an undesirable manner because uneven blasting conditions are the result, whereby it becomes impossible to achieve a defined, reproducible blasting effect on the surface of the work piece. Besides, the expensive hose conduit structure constitutes a constant source of trouble and even dangers.